US 4,428,055 AGranted

Tool touch probe system and method of precision machining

AssigneeGeneral Electric Company

InventorsJohn R. Zurbrick, John R. Kelley

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Abstract

A system and method are disclosed for automatically machining a work piece to precise selectively determined dimensions under computer numerical control in which the cutting tool is set automatically and automatic on-machine inspection is performed of the machined work piece surfaces. Using vibration sensing to detect contact between the cutting edge of the cutting tool and position reference surfaces, the cutting edge is calibrated against these surfaces under closed loop control. The deviation between the programmed and the actual positions of the cutting edge at each reference surface is determined and an initial compensating tool position offset is automatically provided in each axis and is entered into numerical control means. After machining has been initiated, probing of the work piece occurs at least once before the final cut is taken. The tool functions as a tool touch probe during this operation and vibrations are sensed as the calibrated cutting edge is brought into contact with the machined surface. Appropriate tool position offsets are determined and entered into the numerical control means at that time, to assure that the dimensions of the finished surface will conform to the desired dimensions. After final machining has taken place, the finished surface is again probed with the calibrated cutting edge, using vibration sensing. Deviations from the desired dimensions are determined and are indicated together with the allowable machining tolerance for each dimension.

Claims36

Dependent claims

A method for precision machining at least one surface of a work piece by means of a programmable, numerically controlled machining system, said system including numerical control means adapted to operate under the direction of a selected machining program, at least one cutting tool and at least first and second reference surfaces adapted to provide a position reference with respect to the origin position of the selected program;

said method comprising:
(1) probing said reference surfaces with a cutting edge of said tool during rapid relative motion therebetween to calibrate the position of said cutting edge in at least first and second axes of motion each normal to one of said reference surfaces;
(2) sensing vibrations transmitted upon the occurrence of probing contact between said cutting edge and the probed reference surface;
(3) signaling the actual contact position of said cutting edge to said numerical control means in each of said axes in response to said sensed vibrations;
(4) storing first deviations in said numerical control means each determined by the difference along one of said axes between the programmed contact position of said cutting edge with the corresponding reference surface and said actual contact position;
(5) storing first compensating offsets in said numerical control means each determined at least in part by one of said first deviations in each axis;
(6) machining said work piece with said tool during rapid relative motion between said cutting edge and said work piece, said machining step being performed under control of said program modified by said first offsets;
(7) probing the machined work piece surface with said cutting edge during rapid relative motion therebetween to provide a measurement at least in one of said axes;
(8) sensing vibrations transmitted upon the occurrence of probing contact between said cutting edge and said machined surface;
and
(9) signaling the actual contact position of said cutting edge in at least said one axis to said numerical control means in response to said last-recited sensed vibrations.

8 more elements

A numerically controlled system for precision machining at least one surface of a work piece to selectively determined final dimensions;

said system comprising:
programmable numerical control means;
machining apparatus including a stationary bed, work piece holding means, and tool holding means adapted to mount one or more tools and to place one of said tools into operating position;
means for providing rapid relative motion between the cutting edge of said tool and said work piece, said tool being adapted when stationed in its operating position to effect the removal of material from said work piece during said rapid relative motion while said cutting edge is forced against said work piece;
means controlled by said numerical control means for positioning said respective holding means relative to each other in at least first and second axes of motion of said machining apparatus;
position feedback means adapted to signal to said numerical control means information representative of the actual position of said holding means at least in said first and second axis respectively;
position reference means associated with said machining apparatus and including at least a pair of position reference surfaces each corresponding to one of said axes, each of said reference surfaces providing a calibrated position reference with respect to the origin position of a machining program adapted to direct the operation of said numerical control means;
and
transducer means positioned to sense vibrations indicative of contact between said work piece or one of said reference surfaces respectively and said cutting edge during rapid relative motion therebetween and being adapted to convert said sensed vibrations to electrical signals;
circuit means coupling said transducer means to said numerical control means adapted to discriminate against spurious signals on the basis of predetermined time domain characteristics, said circuit means being effective to select signals generated by said transducer means in response to vibrations transmitted as a consequence of an actual probing contact between said cutting edge and a surface;
whereby the position of said cutting edge may be calibrated in at least said first and second axes through probing contacts with said reference surfaces during rapid relative motion therebetween and the precision of machining said work piece surface in accordance with said machining program is enhanced by means of modifying compensating offsets determined at least in part by said calibration.

8 more elements

In a numerical control system of the type in which a machine tool includes workpiece holding means for holding a workpiece, tool holding means for holding a tool, a reference surface at a predetermined location with respect to a home position of the tool holding means, positioning motors for effecting relative motion between the tool and workpiece, apparatus for providing a continuous indication of actual tool displacement from the home position and apparatus coupled to the tool for providing a tool touch signal when the tool contacts the reference surface or workpiece is operative in a closed loop mode and in response to a stored program, a method of numerical control operation comprising the steps of:

(a) providing, in response to the stored program, first move command signals to the positioning motors to cause the tool to move from the home position into contact with the reference surface whereby a tool touch signal is generated;
(b) sensing the indicated displacement of the tool from the home position when the tool touch signal is generated;
(c) comparing the indicated tool displacement to a programmed displacement obtained from the stored program;
(d) computing a deviation between the indicated tool displacement and the programmed displacement;
(e) establishing a first tool offset value based upon the computed deviation to compensate for such deviation;
(f) providing, in response to the stored program, a plurality of control signals to effect machining of the workpiece based upon the first tool offset value;
(g) terminating the control signals prior to finish machining of the workpiece;
(h) providing second move command signals to effect movement of the tool into contact with the reference surface;
(i) sensing again the indicated tool displacement from the home position with the reference surface;
(j) re-computing the deviation between the again sensed tool displacement and the programmed tool displacement;
(k) modifying the first tool offset value in accordance with the re-computed deviation;
(l) providing third move command signals to cause the tool to move into contact with the workpiece;
(m) sensing tool contact with the workpiece;
(n) comparing the sensed tool displacement upon contact with the workpiece to the programmed tool displacement;
(o) computing the remaining machining necessary to finish the workpiece based upon said last mentioned comparison and the actual desired dimensions of the workpiece;
and
(p) providing a plurality of control signals to effect finish machining of the workpiece.

14 more elements

Dependencies are inferred from the claim text.